1. Technical Field
The present invention relates to a method for transferring image information.
2. Prior Art
Following techniques have been employed: to equip both of a main body of a computer and a display device with a storage device storing image information, to communicate between them if image information stored in the storage device in the main body of the computer is updated by the main body of the computer and to limit data transferred from the main body of the computer to an updated portion, and to refresh displayed content on the display device with image information stored in the storage device in the display device. For instance, U.S. Pat. No. 5,726,677 discloses that VRAM of the main body of the computer is connected to RAM in an X driver of an LCD module via a special bus and if data of the VRAM is updated, the updated portion is transferred via the special bus. This patent does not disclose any detailed method for transferring the data from the VRAM to the RAM in the X driver of the LCD module.
Japanese Unexamined Patent Application No. Hei 8-179740 discloses that the image generation side thins out and transmits graded data from the frame memory according to a predetermined rule and the image display side stores part of graded data which comprises a preceding image frame based on the rule to complement the transmitted graded data with the stored graded data. For instance, on the image generation side, if high order bit data of the graded data of the preceding image frame is identical, a signal representing the identity and low order bit data are transferred, and if it is not identical, a signal representing the non-identity and high order bit data are transferred. Meanwhile, on the image display side, high order bit data of the preceding image frame is stored, and the graded data is complemented by transmitted low order bit data and stored high order bit data if the signal representing the identity is received, and the graded data is complemented by transmitted high order bit data plus preset constant data as low order bit data if the signal representing the non-identity is received.
Another technique to transfer image information divided into several frames has been employed. Japanese Unexamined Patent Application No. Hei 4-86190 discloses that source data for display is thinned out at every predetermined number n and read out and then transferred. For instance, it is disclosed that every one of n lines are transferred and the transmission speed is 1/n.
Furthermore, Japanese Unexamined Patent Application No. Hei 6-22303 discloses that a frame is divided into a plurality of subframe areas and only divided single frame area is transmitted for each frame with thinning out. This allows a plurality of subframes to reproduce the original single frame, to decrease the load on the display side by transferring only changed portions (differences) between frames as well as significantly reducing transmission capacity. In addition, transmission volume is further reduced by using a compression. However, the transmitting and receiving sides must execute more complicated processing.
Meanwhile, there exists a technology called gradation emulation. It does not represent a plurality of gradation levels in a single frame but represents them over a plurality of frames, often using a dither pattern. For instance, U.S. Pat. No. 5,712,651 discloses that it comprises 16 dither matrixes corresponding to 16 levels of gradation. In addition, in order to prevent flickers on the display screen, a dither matrix is provided for each frame. At gradation level 1, 16 dither patterns corresponding to the frames 1 to 16 are provided, one dot of which lights up. In this patent, dither matrixes are used for gradation emulation and not for updating image information stored in the display.
Also, with regard to a ferrodielectric liquid crystal display, there exists a technology to check, when partial writing to a display memory occurs, the number of displayed lines whose display data was changed by the partial writing and to write partially to the ferrodielectric liquid crystal display only if the number of changed lines is equal to or less than a predetermined number (for instance, U.S. Pat. No. 5,629,717/Japanese Patent Publication No. 2617345). This technology is a specific technology to ferrodielectric liquid crystal displays.
Furthermore, also with regard to ferrodielectric liquid crystal displays, there exists a technology comprising a flag memory which represents whether or not each line was rewritten and a flag counter which calculates the number of flags of the flag memory on the full screen, wherein the full screen is refreshed if the number of the flags is up to one, and partial rewriting is performed if it is between two and four, and the full screen is refreshed if it is equal to or more than five (for instance, Japanese Unexamined Patent Publication No. Hei 5-241528). This patent also describes that some lines may not be refreshed if a partial rewriting mode continues, in which case the threshold is to be changed. This technology is also specific to ferrodielectric liquid crystal displays.
As seen in the above background arts, there is none in which a dither matrix is used for updating images stored in a display device in transferring image information between the main body of a computer and the display device. In addition, it is not mentioned that, also in transferring image information between the main body of a computer and the display device, the image information stored in the main body of a computer is divided into a plurality of blocks, the number of pixels whose data is changed or rewritten is counted for each block, and the image information in blocks exceeding a predetermined number is transferred to the display device block by block.
Thus, an object of the present invention is to enable transfer of image information of high resolution via a transmission line with limited width by using a simple mechanism.
In addition, another object of the present invention is to enable more natural display of image information transferred via a transmission line with limited band width by using a simple mechanism.
In addition, still another object of the present invention is to reduce power consumption and unnecessary radiation by lowering transmission rate of image information.
The present invention is to be handled as follows. If first image information which is stored in a first apparatus and comprises a plurality of pixels is transferred to a second apparatus in order to update second image information stored in the second apparatus, following steps are performed: defining a plurality of blocks in the first image information, wherein each block has a size of a predetermined dither matrix; and transferring each pixel information in each block to the second apparatus in order of a value of a corresponding element of the dither matrix. By transferring in order of a value of a corresponding element in the dither matrix, it becomes possible to transfer image information of high resolution even if the transmission line has low band width and to update and display image information in a natural form in the second apparatus. Moreover, it is also possible to put each pixel an order of transfer before transferring and to transfer them in that order thereafter.
The second aspect of the present invention is as follows. That is, if image information which is stored in a first apparatus and comprises a plurality of pixels is transferred to a second apparatus, wherein the pixels are divided into blocks, and each block has a size of a predetermined dither matrix, following steps are performed: determining, in order of a value of a corresponding element in the dither matrix, whether each pixel in each block of the image information should be transferred to the second apparatus; and transferring information of the pixels which are determined to be transferred in the order to the second apparatus. In this way, it is possible to avoid information transfer of unnecessary pixels, whereby the amount of transferring data is reduced. It may further include a step of changing a bit which corresponds to image information of a pixel changed by the first apparatus and represents whether the pixel is changed or not (written or not) to a state of changed (written).
In this case, the first apparatus may have a bit representing whether there is a writing to the pixel for each pixel, and the above determining step may include a step of referring to the bit of the pixel to be determined. It is also possible to include a bit representing whether there is a change, not writing, and a step of referring to the bit.
If there is information of pixels not to be transferred, it further includes a step of transferring to the second apparatus information representing whether each pixel is transferred or not. This information representing whether each pixel is transferred or not may be xe2x80x9c1xe2x80x9d in case of transferring bit by bit, and xe2x80x9c0xe2x80x9d in case of not transferring. In addition, this information representing whether each pixel is transferred or not may be a bitmap of the entire image information, a bitmap of pixels in the same order in different blocks, a run length of pixels included in the same line among the pixels in the same order as above in different blocks. Note information representing whether each pixel is transferred or not can be shared with information representing whether the pixel is changed or written.
Furthermore, it is also possible to include a step of performing, in said first apparatus, a processing for moving a portion of the image information to another part in the image information; and a step of transferring to the second apparatus a command for performing the same processing for moving. In this way, it is possible to reduce the amount of data to be transferred, which is less than changed pixels. In this case, a following step may be further included: a step of moving the content of bits which correspond to the moved portion of the image information, each of which represents whether a change (writing) of a pixel is made, to a position for another portion of the image information in bits, each of which represents whether a change (writing) of a pixel is made. It is also possible to include a step of determining whether a pixel to be transferred is included in a group comprising one or a plurality of the blocks; and if it is determined that no pixel is to be transferred, skipping the step of determining whether each pixel in each block of the image information and the subsequent steps for a predetermined pixel in the group. In this way, the amount of transferring data may be further reduced.
The step of determining whether a pixel to be transferred is included in a group may comprise a step of referring to a bit for each group, wherein the bit represents whether a pixel in the group is updated by the first apparatus.
The third aspect of the present invention is as follows. That is, if image information which is stored in a first apparatus and comprises a plurality of pixels is transferred to a second apparatus, wherein the plurality of pixels is divided into blocks, and each block has a size of a predetermined dither matrix, following steps are performed: holding change information representing whether content of each pixel in the image information is changed; determining, in order of a value of a corresponding element in the dither matrix, whether each pixel in each block of the image information should be transferred to the second apparatus, by referring to the change information; and transferring the pixels which are determined to be transferred in the order to the second apparatus.
If the second image information stored in the second apparatus which receives the transmitted information is updated, following steps are performed: receiving information of each pixel in each block of the first image information in order of a value of a corresponding element in the dither matrix; and updating information of a corresponding pixel in the second image information with information of each pixel received. The second image information is updated in order of receipt, but the order in which the display screen is refreshed in the second apparatus may be asynchronous with the order in which it is updated.
If by using first image information which is stored in a first apparatus and comprises a plurality of pixels divided into blocks, each of which block has a size of a predetermined dither matrix, second image information stored in a second apparatus is updated, following steps are performed: receiving information of each pixel in each block of the first image information, except information not transferred from the first apparatus, in order of a value of a corresponding element in the dither matrix; and updating information of a corresponding pixel in the second image information with information of each pixel received. As it is received in order of a value of a corresponding element in the dither matrix, when the second image information is updated, consequently the display screen of the second apparatus is refreshed in a visually natural way.
The above receiving step includes a step of receiving information representing whether or not each pixel is transferred to synchronize with the first apparatus of the transmitting end.
It is also possible to further include a step of receiving a command for moving a portion of the second image information to another portion in the second image information and a step of moving a portion of the second image information to another portion in the second image information according to the command.
It is also possible that groups which comprises one or a plurality of blocks are defined and the above receiving step include a step of receiving information representing which groups information of transferred pixels belongs to. Because the amount of transferring data is further reduced, it is intended to grasp which pixel""s information has been transferred to exactly update the second information.
The fourth aspect of the present invention is as follows: That is, if image information comprising a plurality of pixels stored in a first apparatus and divided into a plurality of blocks is transferred to a second apparatus, following steps are performed:
counting the number of changed pixels for each block; determining for each block whether the count exceeded a predetermined threshold; and if the count of a block exceeded the predetermined threshold, transferring to the second apparatus, information of the pixels belonging to the block. According to this fourth aspect, any change of a pixel made by the first apparatus is not immediately transferred to the second apparatus. In the event that the number of pixels which are changed is small, however, the impact on the second apparatus is slight, and even if a change of an influential scale is made, there is no problem because the transfer is made by the block.
The fifth aspect of the present invention is a method for transferring image information comprising a plurality of pixels stored in a first apparatus and divided into a plurality of blocks, to a second apparatus. The method comprises the steps of:
counting the number of writings to pixels for each block; determining for each block whether the count exceeded a predetermined threshold; and if the count of a block exceeded the predetermined threshold, transferring to said second apparatus, information of the pixels belonging to the block. In this case, it is determined based on a writing, not a change. The change is counted only in the event of writing information different from previous one on the same pixel, while even a writing of the same information is counted in case of a writing. Theoretically it should be based on changes rather than writings, but there is a drawback that detecting changes requires great load.
If the count is determined not to have exceeded the predetermined threshold, it is possible to increment the count. This is for the purpose of preventing the situation where the count value does not exceed a predetermined threshold no matter how often the count value of a certain block is checked and the screen is never updated. That is, it must be transferred by the block at least once in several times.
While the above describes the present invention as processes, it is possible to implement the present invention by an apparatus which perform these processes or to create a program which causes a computer to perform these processes. This program is typically stored on storage medium such as a floppy-disk and a CD-ROM or any other form of storage device.